It has been common practice in the electrical wiring trade to mount transformers, such as low voltage bell and control transformers, on electric junction boxes or on covers for electric junction boxes. The mounting arrangement provides for connecting the line voltage portion of the transformer within the junction box, while leaving the low voltage or control portion of the transformer external to the junction box. In some cases it has been possible to mount the transformer directly through a knockout in the side of a conventional junction box. In other cases, there is not sufficient space for this type of mounting where the transformer is of a larger capacity needed for many control applications, such as heating and air conditioning control. In these cases, the control transformer has been mounted on top of a conventional octagon, 2 .times. 4 or 4 .times. 4 box. In some cases, the transformer has been mounted on a flat plate-like member that forms an enclosure for the electric junction box by providing an opening in the cover that is annular in configuration and which accepts either a mounting spud that forms part of the transformer end bell or accepts some other type of mounting means that clamps the end bell of the transformer into the hole in the mounting plate. In some cases the transformer is manufactured with the mounting plate as an integral part of the transformer, and with the transformer recessed into an opening in the plate.
The different types of mounting configurations have in the past required an assortment of different types of transformers and mounting plates. In some cases where the transformer is surface mounted on the plate through a hole, the amount of room taken by the transformer outside of the electric enclosure has been excessive. To overcome this, there has been manufactured a line of transformers in which the transformer is recessed into the plate and where the transformer and plate are sold as an integral unit. These arrangements require an installer to stock a number of different transformers and plate configurations in order to accomplish the end result of mounting a low voltage control transformer in a system in a manner that is compatible to the space available.